It is well known in the field of hydraulic engineering, that there is an ongoing need to reduce or inhibit erosion caused by rivers, streams, and other waterways that are both natural and man-made. The causes of erosion are many, coming about where there is a change in grade or various man-made devices that impart a high level of fluid energy into the fluid flow. This has been recognized in the prior art as there are various types of hydraulic energy dissipation devices or apparatus which are commonly referred to under the collective term “energy dissipators”, and are used to provide erosion control protection by serving as, among other things, dam energy dissipating basins, dropped structures in natural streams, man-made channels, and gate control structures in natural streams or man-made channels. The significant resources devoted by many governmental and private agencies to protect civil structures such as canals, dams, or other waterways constructed of earth materials or man-made materials from erosion has resulted in the development of a relatively wide range of prior art fluid energy dissipation and other erosion protection systems.
One significant category of open channel flow prior art fluid flow energy dissipators is termed a “hydraulic jump” in the hydraulic engineering arts, and utilizes non uniform flow which occurs when supercritical flow has its velocity reduced to sub critical flow. In an open flow channel, or more particularly an energy dissipating basin for instance, the hydraulic jump is intentionally created, typically forming where the design energy dissipating basin floor slope changes from steep to level or near level in the downstream direction as on the apron base of an energy dissipating basin. The hydraulic jump is characterized by a discontinuity of the fluid surface with a steep upward slope in the downstream direction, with the fluid surface appearing to have highly turbulent flow. The hydraulic jump in this instance serves a useful purpose, for it dissipates much of the destructive energy of the high velocity fluid, thereby reducing downstream erosion. Unfortunately, however, the hydraulic jump can create undesirable rotating eddy currents that occur in the rise in the water surface slightly downstream of the slope change wherein the fluid is transitioning from a high velocity to a lower velocity. The rise in water surface being observed to have violent turbulence with under the surface rotating eddy currents that result in the fluid flowing in a downstream direction then reversing direction and flowing in a upstream direction, then subsequently reversing direction again and flowing in the downstream direction in a somewhat elliptical path thus causing a dissipation of fluid energy. If the rotating eddy currents are either contained within the fluid flow or do not cause other problems, then they are not usually of concern. Thus, the overall objective of the hydraulic jump is to reduce the velocity of the fluid flow downstream of the hydraulic jump in a manner to minimize erosion damage to the open flow channel from high fluid flow velocities.
Given the desirability of the hydraulic jump, the next critical factor in hydraulic engineering is to control the position or location of the hydraulic jump and thus the rotating eddy currents within the open channel given the objective of minimizing erosion damage due to high fluid flow velocities in the open channel. Controlling factors are the rate of grade transition change of the flow channel, the differential in fluid velocities, and the sizing of the flow channel, all of which can be accounted for in the hydraulic engineering design. However, there is another complicating factor in that for a fixed grade transition change, fixed fluid velocity differential, and fixed flow channel sizing, there is also the issue of a significant variances in fluid flow rate within the fixed flow channel in going from 0 percent to 100 percent that can cause the hydraulic jump position and severity in fluid flow velocity differentials, and the location and size of the rotating eddy currents to change. In other words, the aforementioned fixed factors are in reality optimized for the hydraulic jump to properly dissipate energy at a particular fixed flowrate, and when deviations occur from this fixed flowrate either being higher or lower, results in compromise of the beneficial effect of the hydraulic jump in dissipating kinetic fluid energy, thus possibly increasing the erosion damage to the open flow channel. This is because, with changes in flowrate, not only the fluid velocities change but also the position and size of the rotating eddy current which can result in increased erosion and/or abrasion of the open flow channel, due for instance from the depositing of streambed material into the energy dissipating basin, wherein the streambed material erodes and/or abrades the energy dissipating basin from the high velocities and turbulence of the fluid.
One prior art solution disclosed in U.S. Pat. No. 1,561,796 to Rehbock focused upon the destructive effect of high fluid flow velocities existing at the outlet of the energy dissipating basin wherein the earth streambed would suffer a high degree of erosion directly adjacent to the energy dissipating basin outlet. Rehbock utilized what is called an “apron” or end sill that was positioned directly adjacent to the energy dissipating basin outlet floor. This apron was designed to create a ground eddy that was positioned just above the earth streambed that created the effect of a reverse direction flow, in other words an upstream flow just over the earth streambed directly adjacent to the apron. In addition, flow gaps in the apron allowed thin jets of water running in the normal downstream direction to counteract the reverse flow eddy in an attempt to create a near zero fluid flow velocity upon the earth streambed directly adjacent to the apron. The gaps also allowed sediment that was trapped in the energy dissipating basin to flow through the outlet of the energy dissipating basin and not be trapped in the energy dissipating basin. The shortcoming of Rehbock is related to the situation wherein the fluid flow rate varies greatly causing the ground eddy to change in position, size, and velocity that could cause earth streambed erosion and/or trap earth streambed sediment in the energy dissipating basin that was unable to exit the energy dissipating basin through the outlet gaps.
This problem was also recognized in the U.S. Pat. No. 2,103,600 to Stevens that discloses a plurality of baffle blocks that are arranged in rows in addition to being staggered with respect to the individual blocks in an adjacent row with the baffle blocks being mounted on the upstream side and adjacent to the end sill or outlet of the energy dissipating basin. Stevens's goal was to create a reverse eddy flow on the floor of the earth streambed directly adjacent to the energy dissipating basin outlet to redeposit earth and streambed sediment against the energy dissipating basin outlet to prevent undermining or loss of earth streambed material directly adjacent to the energy dissipating basin outlet while accommodating different fluid flow rates. Similar to Stevens, in U.S. Pat. No. 6,059,490 to Kauppi, also disclosed is a plurality of blocks that are arranged in rows and stacked upon each other in a shingle like overlap such that the blocks of each row are offset relative to the blocks of each adjacent row. Kauppi states that these blocks impart perpendicular velocity components in the fluid flow relative to the downstream direction of fluid flow, thus creating additional turbulence, which results in more kinetic energy dissipation of the fluid flow.
What is needed is a structure mounted within the energy dissipating basin that is operational to control the reverse flow eddy that occurs directly adjacent to the energy dissipating basin outlet apron over and just above the earth streambed while at the same time accommodating the changes in the position, size, and velocity of the reverse flow eddy that occur with changes in fluid flowrate in the energy dissipating basin resulting in the minimization of damage to both the energy dissipating basin itself and the earth stream bed. Ultimately, the purpose is two fold with the desired structure, firstly, is to not to disturb the earth stream bed either by allowing a washout of the earth streambed material adjacent to the energy dissipating basin outlet causing an undermining in this area and secondly, to help prevent the depositing of earth streambed material into the energy dissipating basin itself wherein the stream bed material becomes trapped in the energy dissipating basin and remains in an agitated state from fluid flow turbulence causing a high degree of erosion and/or abrasion on the energy dissipating basin itself.